Semiconductor memory device using bus inversion scheme

ABSTRACT

A semiconductor memory device is capable of transferring address signals at high speed and improving the operation reliability even though an input rate of an address signal increases, and thus a degradation of an operation speed caused by applying a bus inversion scheme can be prevented and power consumption can be reduced. The semiconductor memory device includes a bus inversion decoding block configured to determine whether a plurality of address signals are inverted or not by decoding an indication control signal, and an address buffer block configured to receive two address signals per one cycle of an external clock, align the received address signals for parallel processing, and transfer the address signals or inverted address signals according to an output of the bus inversion decoding block.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present patent application is a Divisional application claiming thebenefit of application Ser. No. 12/150,670, filed Apr. 30, 2008 now U.S.Pat. No. 7,773,737.

The present invention claims priority to Korean patent applicationnumber 10-2007-0111529, filed on Nov. 2, 2007 which is incorporated byreference in its entirety.

BACKGROUND OF THE INVENTION

The present invention relates to a high-speed semiconductor memorydevice, and more particularly to a semiconductor memory device operatingwith an address to which a bus inversion scheme is applied.

In a system with a variety of semiconductor devices, a semiconductormemory device serves as data storage. The semiconductor memory deviceoutputs data corresponding to addresses received from a data processor,e.g., a central processing unit (CPU), or stores data received from thedata processor into unit cells selected by addresses inputted togetherwith the data.

As the operating speed of the system is increasing, the data processorrequires the semiconductor memory device to input and output data athigher speed. To this end, internal circuits of the semiconductor memorydevice must be able to operate at high speed and transfer signals ordata therebetween at high speed.

The operating speed of the semiconductor memory device can be increasedby performing internal operations at higher speed or increasing thesignal and data input/output speed. As one example, a double data rate(DDR) memory device can increase the data output speed by outputtingdata in synchronization with a falling edge as well as a rising edge ofa system clock. Since the DDR memory device inputs and outputs two dataper clock cycle via one input/output terminal in one cycle, its datainput/output speed is faster than that of the existing semiconductormemory device. Recently, a semiconductor memory device capable ofinputting or outputting four data in one cycle of a system clock wasproposed. Although the data input/output speed of the semiconductormemory device is gradually increasing, an input/output speed of anaddress or command signal is unsatisfactory.

In a typical semiconductor memory device, an address is inputtedtogether with an external operation command signal in synchronizationwith a rising edge of a clock. That is, the semiconductor memory devicereceives external address and operation command signal insynchronization with a rising edge of an external clock and performs aninternal operation. However, as the operating speed of the semiconductormemory device is increasing, an address can be inputted two times in onecycle of the system clock.

Graphics double data rate version 5 (GDDR5) memory devices for graphicworks are designed to receive addresses at a rising edge and a fallingedge of an external clock. That is, the GDDR5 memory devices can receivethe addresses two times in one cycle of the external clock. Thus,compared with the typical semiconductor memory device, the number ofaddress pins is reduced or the operating speed can be increased byconnecting extra pins to a power voltage terminal or a ground terminal.Since an external operation command signal is still inputted insynchronization with a rising edge of an external clock, the addressinput speed is two times faster than a command input speed.

Since the addresses are inputted two times in one cycle of the externalclock, the address transition increases two times and a voltage togglingoften occurs at the address input port, causing a lot of currentconsumption. As one example, a swing width of an address signal can bedefined in a range from VIH(Vref+0.12V) at a logic high level toVIL(Vref−0.12V) at a logic low level. Therefore, if the transitionsoccur two times more than the conventional art, the power consumptionwill also increase.

As the signal input speed increases in the same time, a bus inversionscheme is applied to the semiconductor memory device in preparation forthe increasing transitions. According to the bus inversion scheme, apreviously transmitted value and a current value to be transmitted arecompared with each other. When transitions occur more than half of atotal bit number to be transferred, a signal transmitter transmits aninverted value of the current value to be transmitted, and a signalreceiver recognizes the current value by inverting the received signal.On the other hand, when transitions occur less than half of the totalbit number, the signal transmitter transmits the current value and thesignal receiver recognizes the received signal as it is. At this point,the signal transmitter and the signal receiver additionally transmitindication control signals indicating whether they transmit the currentvalue or its inverted value.

A case where the bus inversion scheme is applied to 8-bit bus will bedescribed in more detail. For example, assuming that “00011100” is apreviously transmitted signal and “00001010” is a current value to betransmitted, a transition should occur at 3 bits. In this case, sincethree bits of the total eight bits have only to be changed, the signaltransmitter transmits the current value to be transmitted. If a value tobe newly transmitted after the transmission of “00001010” is “11100111”,transmission should occur at six bits. In this case, transitions occurmore than half of the total eight bits, thus increasing the powerconsumption. Therefore, using the bus inversion scheme, the signaltransmitter inverts the values “11100111” to be transmitted, andtransmits “00011000”. The signal transmitter activates the indicationcontrol signal and indicates that the transmitted value is the invertedvalue. In this manner, compared with the previously transmitted value“00001010”, transitions occur at 2 bits of the eight bits. Consequently,the power consumption can be reduced, compared with the case where thetransitions occur at six bits.

If such a bus inversion scheme is applied to multi-bit address signalsinputted from the outside, an address input rate is increasing and thepower consumption is reduced. However, when carrying out the businversion scheme, an operation speed may be lowered, or an operationmargin for internal operation may be reduced, degrading the wholeoperation stability of the semiconductor memory device. In particular,if a delay occurs in the input of the address signal, an operation ofreading data from or writing data to a cell corresponding to an addresssignal becomes slow, degrading the performance of the semiconductormemory device.

SUMMARY OF THE INVENTION

Embodiments of the present invention are directed to providing ahigh-speed semiconductor memory device capable of transferring addresssignals at high speed and improving the operation reliability. Eventhough an input rate of an address signal increases, a setup/hold timenecessary to receive the address signal can be sufficiently ensured.Thus, a degradation of an operation speed caused by applying a businversion scheme can be prevented and power consumption can be reduced.

In accordance with an aspect of the present invention, there is provideda semiconductor memory device for including a bus inversion decodingblock configured to determine whether a plurality of address signals areinverted or not by decoding an indication control signal, and an addressbuffer block configured to receive two address signals per one cycle ofan external clock, align the received address signals for parallelprocessing, and transfer the address signals or inverted address signalsaccording to an output of the bus inversion decoding block.

In accordance with another aspect of the present invention, there isprovided a system for including a data processor configured to compareprevious address signal with current address signal respectively, andoutput the current address signals or inverted current address signalsas address signals according to the comparison result together with acommand signal, and a semiconductor memory device configured to ensure asetup/hold time by aligning the address signals for parallel processing,and perform an operation corresponding to the command signal bytransferring the address signals according to an inversion informationof the address signals using indication control signals indicating theinvention information.

In implementing an address bus inversion (ABI) scheme by applying a businversion scheme to an address in order for increased operation speedand reduced power consumption, a pulse capable of ensuring an operationmargin of an address buffer is generated by using an indication controlsignal for ensuring the reliability in a latching operation of anaddress signal. The use of this pulse can prevent a degradation of asetup/hold time at an input port caused by the increase of the inputrate of the address signal. Furthermore, the semiconductor memory devicecan stably receive the address signal, while preventing the degradationof the operation speed. Moreover, the pulse generator can be designedwithout great modification of the existing input buffer and latch,thereby ensuring the operation stability of the semiconductor memorydevice.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a semiconductor memory device in accordancewith an embodiment of the present invention.

FIG. 2 is a signal timing diagram illustrating the operation of thesemiconductor memory device of FIG. 1.

FIG. 3 is a schematic circuit diagram of a first falling clocksynchronizer of FIG. 1.

FIG. 4A is a schematic circuit diagram of a first address buffer of FIG.1.

FIG. 4B is a schematic circuit diagram of a second address buffer ofFIG. 1.

DESCRIPTION OF SPECIFIC EMBODIMENTS

Hereinafter, a semiconductor memory device using a bus inversion schemein accordance with the present invention will be described in detailwith reference to the accompanying drawings.

FIG. 1 is a block diagram of a semiconductor memory device in accordancewith an embodiment of the present invention.

Referring to FIG. 1, the semiconductor memory device includes a businversion decoding block 50 and an address buffer block 80. The businversion decoding block 50 includes a signal input buffer 10, a risingclock synchronizer 20, and first and second falling clock synchronizers30 and 40. The bus inversion decoding block 50 decodes an indicationcontrol signal ABI and controls the address bus block 80. The addressbuffer block 80 includes first and second address buffers 60 and 70. Theaddress buffer block 80 transfers addresses according to a controlsignal outputted from the bus inversion decoding unit 50.

The signal input buffer 10 receives the indication control signal ABIfrom the outside. The indication control signal ABI indicates whetherthe inputted address signal has an original value or an inverted valueaccording to the address bus inversion scheme. The indication controlsignal ABI inputted to the signal input buffer 10 is outputted as anindication signal OUT and a complementary indication signal OUTB. Whenthe indication control signal ABI is at a logic low level, theindication signal OUT has a ground voltage level VSS and thecomplementary indication signal OUTB has a power supply voltage levelVDD.

The indication signal OUT is inputted to the rising clock synchronizer20. The rising clock synchronizer 20 latches the indication signal OUTusing an internal rising clock CLKABIR synchronized with a rising edgeof an external clock CLK. Thus, the indication signal OUT becomes arising indication signal OUTR synchronized with the rising edge of theexternal clock. The rising indication signal OUTR from the rising clocksynchronizer 20 and the complementary indication signal OUTB from thesignal input buffer 10 are inputted to the first falling clocksynchronizer 30 and the second falling clock synchronizer 40,respectively.

Like the rising clock synchronizer 20, the first and second fallingclock synchronizers 30 and 40 latches the rising indication signal OUTRand the complementary indication signal OUTB using an internal fallingclock CLKABIF synchronized with a falling edge of the external clockCLK. Thus, the rising indication signal OUTR and the complementaryindication signal OUTB are synchronized with the falling edge of theexternal clock CLK. Thereafter, the first falling clock synchronizer 30outputs a rising inversion enable signal ABIRON and a rising inversiondisable signal ABIROFF synchronized with the falling edge of theexternal clock CLK according to a value of the rising indication signalOUTR. The second falling clock synchronizer 40 outputs a fallinginversion enable signal ABIFON and a falling inversion disable signalABIFOFF synchronized with the falling edge of the external clock CLKaccording to a value of the complementary indication signal OUTB.

The internal rising clock CLKABIR and the internal falling clock CLKABIFare generated by a clock buffer 90. The clock buffer 90 receives theexternal clock CLK and an inverted external clock, i.e. an externalcomplementary clock, CLKB and outputs the internal rising clock CLKABIRsynchronized with the rising edge of the external clock CLK and theinternal falling clock CLKABIF synchronized with the falling edge of theexternal clock CLK. In order to generate the internal signalssynchronized with the rising edge and the falling edge of the externalclock CLK, a phase of the external clock CLK may be divided, or aninverted external clock may be used. Alternatively, an external clockand its inverted clock independently inputted from the outside may beused.

The rising inversion enable signal ABIRON and the rising inversiondisable signal ABIROFF, which are outputted from the first falling clocksynchronizer 30, are inputted to the first address buffer 60. The risinginversion enable signal ABIRON and the rising inversion disable signalABIROFF are used for determining whether to buffer the address inputtedin synchronization with the rising clock of the external clock CLK, orthe inverted value of the inputted address. In a similar manner, thesecond address buffer 70 buffers the address inputted in synchronizationwith the falling clock of the external clock CLK, or the inverted valueof the inputted address according to the falling inversion enable signalABIFON and the falling inversion disable signal ABIFOFF.

FIG. 2 is a signal timing diagram illustrating the operation of thesemiconductor memory device of FIG. 1.

Referring to FIG. 2, the semiconductor memory device in accordance withthe embodiment of the present invention receives two addresses A<0:1>from one address input port in one cycle of the external clock CLK. Thatis, a 2-bit address signal is inputted through one pad (address pin). Inaddition, the indication control signal ABI is also inputted with theaddress signal. It is assumed in FIG. 2 that the indication controlsignal ABI of “L, H, L, H, L, H” is inputted with six successiveaddresses. This means that 0^(th), 2^(nd) and 4^(th) addresses of thesix successive addresses are inverted signals, and 1^(st), 3^(rd) and5^(th) addresses are original signals.

The 0^(th) address inputted at the rising edge of the external clock CLKis first latched (LAT_AN<0>). Then, the 1^(st) address inputted at thefalling edge of the external clock CLK and the latched 0^(th) addressare latched at the falling edge of the external clock CLK (AT_F<1> andAT_R<0>). That is, two addresses inputted through one address pin in onecycle of the external clock CLK are latched in parallel. Thus, asillustrated in FIG. 1, the two addresses are inputted to the first andsecond address buffers 60 and 70, respectively.

The first and second address buffers 60 and 70 receive the 0^(th) and1^(st) addresses and output the addresses or the inverted addressesaccording to the rising inversion enable signal ABIRON, the risinginversion disable signal ABIROFF, the falling inversion enable signalABIFON, and the falling inversion disable signal ABIFOFF, which areoutputted by decoding the indication control signal ABI. In FIG. 2,since the 0^(th) address is the inverted address signal, the inputtedaddress should be again inverted. Thus, the rising inversion enablesignal ABIRON is activated to a logic high level and the inputtedaddress is inverted. Since the 1^(st) address is the original addresssignal, the falling inversion disable signal ABIFOFF is activated andthe inputted address is transferred as it is.

FIG. 3 is a schematic circuit diagram of the first falling clocksynchronizer 30 of FIG. 1.

Referring to FIG. 3, the first falling clock synchronizer 30 is designedbased on a cross-coupled latch. When the rising indication signal OUTRis a logic high level, the rising inversion disable signal ABIROFF isactivated in synchronization with the internal falling clock CLKABIF.The internal falling clock CLKABIF is outputted from the clock buffer 90in synchronization with the falling edge of the external clock CLK. Onthe other hand, when the inverted signal OUTRB of the rising indicationsignal OUTR is a logic high level, that is, the rising indication signalOUTR is a logic low level, the rising inversion enable signal ABIRON isactivated.

Although the internal configuration of the first falling clocksynchronizer 30 is illustrated in FIG. 3, the rising clock synchronizer20 and the second falling clock synchronizer 40 can also be designed thesame as the configuration of FIG. 3, except the inputted signals. In thecase of the rising clock synchronizer 20, the indication signal OUT fromthe signal input buffer 10 can be latched in synchronization with theinternal rising clock CLKABIR, which is synchronized with the risingedge of the external clock CLK, and then outputted as the risingindication signal OUTR.

FIG. 4A is a schematic circuit diagram of the first address buffer 60 ofFIG. 1, and FIG. 4B is a schematic circuit diagram of the second addressbuffer 70 of FIG. 1. The first and second address buffers 60 and 70 mayhave the same configurations, except the inputted signals.

Referring to FIG. 4A, the first address buffer 60 includes a firstinverter 62, an address transfer unit 64, a latch 66, and a secondinverter 68. The first inverter 62 is configured to invert a risingaddress ADDRESS_R inputted in synchronization with the rising edge ofthe external clock CLK. The address transfer unit 64 is configured totransfer an output of the first inverter 62 or the rising addressADDRESS_R. The latch 66 is configured to latch an output of the addresstransfer unit 64. The second inverter 68 is configured to inverter anoutput of the latch 64. More specifically, the address transfer unit 64includes two transfer gates that are controlled by the rising inversionenable signal ABIRON and the rising inversion disable signal ABIROFF.The address transfer unit 64 transfers the rising address ADDRESS_R orits inverted address according to the logic level of the indicationcontrol signal ABI.

The second address buffer 70 of FIG. 4B is implemented with the sameconfiguration as the first address buffer 60. However, in the case ofthe second address buffer 70, a falling address ADDRESS_F is inputted insynchronization with the falling edge of the external clock CLK, and theaddress transfer unit 74 is controlled by the falling inversion enablesignal ABIFON and the falling inversion disable signal ABIFOFF. Sincethe inverters 72 and 78 and the latch 76 of FIG. 4B have the samefunctions as those of FIG. 4A, their detailed description will beomitted.

As described above, the semiconductor memory device in accordance withthe embodiment of the present invention can use the existing latchcircuit and buffer circuit to control the input of the addresses. Thus,even though the input rate of the address signal increases two times,the setup/hold time in the address input is not influenced.

Furthermore, since the inputted address signal is synchronized with theexternal clock CLK, it is recognized as having a valid window of 1 tCKin view of the internal circuit. Consequently, since both the latchedaddress and its inverted address have the valid window of 1 tCK evenbased on the indication control signal ABI, it is very advantageous toensuring the setup/hold time in the address input. Accordingly, eventhough the inputted value is changed by the indication control signalABI, the address finally transferred to the internal circuit does nothave an additional delay. When used in the general operations (e.g.,operations by active/read/write commands), they can ensure the operationmargin.

As described above, in high-speed semiconductor memory devices thatreceive two addresses in one cycle of an external clock and can reducepower consumption using a bus inversion scheme, a skew that may occur inan address input can be minimized and a setup/hold time can be ensuredin accordance with the present invention.

Furthermore, in an operation of transferring an inputted address signalor its inverted signal according a bus inversion scheme, an operationdelay can be eliminated compared with an existing address transferoperation, thereby ensuring a high-speed operation of a semiconductormemory device without affecting the operation margin necessary for theread and write operations.

Moreover, since the bus inversion scheme is applied to the addresssignal without additional delay, the power consumption is reduced andthe number of the address pins is reduced. By connecting extra pins to apower supply voltage or a ground voltage, the operation speed of thesemiconductor memory device can be increased.

While the present invention has been described with respect to thespecific embodiments, it will be apparent to those skilled in the artthat various changes and modifications may be made without departingfrom the spirit and scope of the invention as defined in the followingclaims.

1. A system, comprising: a data processor configured to compare aprevious address signal with a current address signal, and output thecurrent address signal or inverted current address signal as addresssignals according to the comparison result together with a commandsignal; and a semiconductor memory device configured to ensure asetup/hold time by aligning the address signals for parallel processing,and perform an operation corresponding to the command signal bytransferring the address signals according to an inversion informationof the address signals using indication control signals indicating theinversion information.
 2. The system as recited in claim 1, wherein thesemiconductor memory includes: a bus inversion decoding block configuredto determine whether the address signals are inverted or not by decodingthe indication control signals, the indication control signals being1-bit successive inputted signals in synchronization with the addresssignals respectively; and an address buffer block configured to receivetwo address signals per one cycle of an external clock, align thereceived address signals for parallel processing, and transfer theaddress signals or inverted address signals according to an output ofthe bus inversion decoding block.
 3. The system as recited in claim 2,wherein the bus inversion decoding block parallel-processes twoindication control signals inputted in one cycle of the external clock,and outputs a plurality of decoding result signals synchronized withfalling edges of the external clock to the address buffer block.
 4. Thesystem as recited in claim 2, wherein the bus inversion decoding blockincludes: a signal input buffer configured to receive the indicationcontrol signals to generate a plurality of indication signals havingopposite phases; a rising clock synchronizer configured to synchronizeone of the plurality of indication signals with a rising edge of theexternal clock; a first falling clock synchronizer configured tosynchronize an output of the rising clock synchronizer with a fallingedge of the external clock and control a rising address signal inputtedin synchronization with the rising edge of the external clock; and asecond falling clock synchronizer configured to synchronize anotherindication signal with the falling edge of the external clock andcontrol a falling address signal inputted in synchronization with thefalling edge of the external clock.
 5. The system as recited in claim 4,further including a clock buffer configured to receive the externalclock, generate an internal rising clock to the rising clocksynchronizer in synchronization with the rising edge of the externalclock, and generate an internal falling clock to the first and secondfalling clock synchronizers in synchronization with the falling edge ofthe external clock.
 6. The system as recited in claim 4, wherein therising clock synchronizer, the first falling clock synchronizer, and thesecond falling clock synchronizer are implemented with the samecomponents with the exception of input signals.
 7. The system as recitedin claim 4, wherein the first falling clock synchronizer includes across-coupled latch.
 8. The system as recited in claim 4, wherein theaddress buffer block includes: a first address buffer configured toreceive the rising address signal to generate an inverted rising addresssignal, and transfer the rising address signal or the inverted risingaddress signal according to the output of the first falling clocksynchronizer; and a second address buffer configured to receive thefalling address signal to generate an inverted falling address signal,and transfer the falling address signal or the inverted falling addresssignal according to the output of the second falling clock synchronizer.9. The system as recited in claim 8, wherein the first address bufferincludes: a first inverter configured to invert the rising addresssignal; a transfer unit configured to transfer one of an output of thefirst inverter and the rising address signal according to the output ofthe first falling clock synchronizer; a latch configured to latch anoutput of the transfer unit; and a second inverter configured to invertan output of the latch.
 10. The system as recited in claim 9, whereinthe second address buffer is implemented with the same components as thefirst address buffer with the exception of input signals.